1. Field of the Invention
The present invention relates to a high frequency device including a plurality of rectangular waveguide tubes.
2. Description of the Related Art
Conventionally, a high frequency device has been known which transmits high frequency signals using rectangular waveguide tubes. For example, in Japanese Patent Laid-open Publication No. 2004-221718, a high frequency device that performs transmission of high frequency signals is disclosed in which two metal plates are joined and a plurality of rectangular waveguide tubes are formed on the joint surface. In this type of high frequency device, when a phase relationship is required to be maintained between the high frequency signals to be transmitted, the rectangular waveguide tubes are arranged such that line lengths of the rectangular waveguide tubes are equal or the line lengths differ only by an integral multiple of a guide wavelength.
However, in either case, because the line lengths are designed in a fixed manner, the rectangular waveguide tubes cannot be freely designed. Moreover, transmission loss is unnecessarily increased particularly when lines are arranged such that the line lengths are equal, because the line lengths are set to the longest line length.
On the other hand, when the lines are arranged such that the line lengths differ only by an integral multiple of the guide wavelength, variations in loss increase between channels, and degradation of propagation characteristics increases because the line lengths differ due to temperature change.
In other words, when the line lengths of two rectangular waveguide tubes differ, the rectangular waveguide tube with the longer line length is more affected by temperature change. As a result, the phase relationship between high frequency signals differs at an input terminal and an output terminal of the rectangular waveguide tube, thereby degrading the propagation characteristics.